Post-exposure Prophylaxis (PEP)

Post-exposure prophylaxis (PEP) is a type of emergency medication taken after exposure to HIV in order to prevent an infection. If one believes they have been exposed to HIV, they must take PEP within 72 hours of the contact, otherwise the drug’s effectiveness significantly decreases. The sooner one takes PEP within that 72 hour window, the stronger its effect. After initially taking PEP, one must continue taking PEP daily for 28 days. This drug regimen is known as antiretroviral therapy. One must return to their doctor in intervals to do HIV testing while they are on PEP. PEP must be taken after one believes they have been exposed to HIV, and is not the same as PrEP, which is a daily medication taken prior to any contact with the virus. Furthermore, PEP is not a cure for HIV, it is simply a preventative measure administered before the virus can spread throughout the body and take over healthy cells. Additionally, PEP can only prevent HIV, and not any other sexually-transmitted infection.1 


People Suited for PEP

PEP is not the most suitable drug for everyone. It must be taken after exposure to HIV, and within 72 hours of contact with the virus.2 Therefore, PEP works best for individuals who have been exposed to HIV and need some form of emergency medication to prevent the spread of the virus:

  • People who have just been sexually assaulted by someone who is HIV-positive or whose HIV status is unknown
  • People who have been sharing needles and other forms of drug paraphernalia with individuals who are HIV-positive or whose HIV status is unknown
  • People who have been exposed to HIV during sexual intercourse with an HIV-positive partner (For example, the condom broke during sex, or the partners unintentionally exchanged bodily fluids)
  • Health care employees who have been accidentally exposed to HIV

Any of these situations are examples of suitable times for PEP to be administered in order to prevent any sort of HIV infection.  PEP must be taken as soon as possible following any exposure to the virus, and is most effective when taken 72 hours upon contact.3



PEP is considered to be most effective when taken within 72 hours of contact with the virus. Although PEP does not have a 100% effectiveness rate, it is still very high. This effectiveness rate increases the sooner one takes PEP. A study conducted in Brazil in 2002 revealed that PEP reduced the HIV infection rate by 83%, starting at 4.1 cases per 100 patients a year to 0.7 cases per 100 patients a year.4

One can access PEP by going to an emergency room and inquiring about PEP from a physician. An individual can also make an appointment with their doctor so that they can start taking PEP. If one finds that they take PEP after the 72 hour window, although the effectiveness rate is dramatically lower, research has still found that it can lead to a weaker HIV infection and smaller viral load.

All in all, taking PEP after exposure to HIV has been clinically supported to significantly reduce the chances of contracting an HIV infection, but must be taken as soon as possible to increase effectiveness.


Side Effects

PEP is an antiretroviral therapy drug, which is a type of medication given to someone after they have been exposed to HIV. However, it can lead to many unpleasant side effects such as diarrhea, headaches, nausea, vomiting, and fatigue. Although these side effects can be uncomfortable, they are not life-threatening. They usually will last several days and subside after taking PEP for a while longer. One can consult their doctor about these side effects, as well as whether or not PEP has drug interactions with other medications they are already taking.



PEP consists of taking one or more drugs every single day for at least 28 days in order to prevent infection. The cost of PEP can add up to anywhere between $600 to $1000. It is imperative to take PEP within 72 hours of the initial exposure, and to continue taking PEP for the remainder of the month in order to ensure the highest effectiveness. Discussing payments options with one’s health insurance company is necessary before deciding to take PEP.


Concluding Remarks

Potentially being exposed to HIV can be a very stress-inducing and traumatic experience. Fortunately, PEP can significantly reduce the chances of an HIV infection when taken within 72 hours of the initial exposure. PEP must be taken on a daily basis for 28 days following the initial administration of the drug. Additionally, scientific research has revealed that PEP dramatically decreases the rate of HIV infection. One Brazilian study showed a reduction rate of 83%.4 Although PEP helps prevent HIV, it can still cause some mild but unpleasant side effects. These side effects are not serious and usually subside after a few days. Finally, PEP can be very expensive. It is important to manage these medical payments by coordinating between one’s health insurance, physician, and family.



  1. “5 Tips for Using PEP Effectively | Ending HIV NSW.” Ending HIV, 30 Oct. 2018.
  2. “HIV/AIDS.” Centers for Disease Control and Prevention, Centers for Disease Control and Prevention, 23 July 2018.
  3. “Love May Have Another Protector.” PEP, Pep Facts.
  4. “Post-Exposure Prophylaxis - Efficacy.” HIV & AIDS Information:  Introduction to Pharmacokinetics.

Last Updated: 28 November 2018.